The investigator proposes to design and develop a portable system, analogous to a hand held glucose meter, which will permit rapid, convenient blood coagulation testing on freshly drawn samples from patients undergoing anticoagulant therapy. This cost effective system would better help to meet the needs of patients in a climate of prospective reimbursement and earlier release from hospitals. The use of such a system in the physician's office, free standing ambulatory care facility, and in the home, offers the potential for more rapid test turnaround time and consequently better control of therapy in patients with thromboembolic problems. During the Phase I period, a prototype reagent system together with an electronic measurement device will be fabricated, tested, and analyzed for feasibility by BIOTHERM, INC. The system will be based on a sensitive coagulation monitoring technique developed by the principal investigator. TRIANGLE RESEARCH AND DEVELOPMENT CORPORATION will assist in instrument prototyping for the measurement device. Testing with clinical samples will be conducted at the University of North Carolina, Chapel Hill, Memorial Hospital. If the anticipated results confirm the efficacy of the approach, the prototype would be further developed for extensive clinical testing during Phase II.